The present invention relates to a measuring standard having a magnetic scale graduation, which is able to be scanned by a magnetic field-sensitive detector to generate positionally dependent sampled signals. The invention also relates to a positional measuring device in which a measuring standard of this kind is used.
A measuring standard formed of a base member and of a graduation-scale carrier secured thereto, also having a graduation scale, is used in a position-measuring device for measuring the relative position or the relative speed of two objects, which are movable in relation to one another.
The most common manner of securing a graduation-scale carrier to a base member is by adhesive bonding. European Patent 0 624 780 B1 and U.S. Pat. No. 5,325,055 cite the drawbacks of adhesion, and describe measures for achieving a more stable fastening. European Patent 0 624 780 B1 proposes partially welding the graduation-scale carrier, also known as a scale plate, to the base member. The disadvantage associated with the welding is that very high temperatures act on the graduation-scale carrier, since, for a welded connection it is necessary that material of the graduation-scale carrier be melted over its entire thickness. Since this type of melting can adversely affect the area of the graduation scale, the welding operation must be limited to areas outside of the graduation scale. Generally, only a spot or line-type welding can be implemented relatively simply.
U.S. Pat. No. 5,325,055 relates to the securing of a magnetic ring of magnetizable material to the outer surface of a cylinder block. This reference recognizes that the ring did not sit securely enough during adhesion. To overcome this drawback, it was proposed to provide the magnetic ring with a reinforcement ring. This reinforcement ring is also designed to prevent the ring from becoming partially detached or destroyed at high speeds.
Japanese Patent 2-130418 A proposes heat-shrinking a magnetic ring of magnetizable material onto the outer circumference of a drum base body. This method, however, does not prevent the ring from becoming detached at high rotational speeds.
European Patent 0 723 136 A1 describes winding a band of magnetic material in a helical shape onto the surface area of a drum-shaped rotor.
A ring-shaped scale-graduation carrier of magnetizable material is likewise known from Japanese Patent 63-40813 A. The magnetizable material is a plastically bound magnetic material, which is applied to the periphery of a drum. The application is followed by magnetization of the material. To prevent the plastic material from becoming detached from the drum, a T-slot or dovetailed groove is provided as a keyed connection on the drum""s periphery. This measure, however, does not suffice to prevent the relatively elastic plastic material from becoming loose.
To measure linear displacements of a magnetic core element in relation to a coil arrangement, German Patent 198 06 917 A1 describes soldering the core element to a rod.
For a linear measuring device, Japanese Patent 60-323 A describes securing a magnetic wire by soldering it into a groove of a linear carrier member.
German Patent 41 33 709 A1 describes soldering individual pulse generator profiles, which are spaced apart from one another, onto the periphery of a wheel. To produce each pulse used in incremental positional measurements, a separate element in the form of a piece of wire is aligned with the periphery and secured thereto.
U.S. Pat. No. 5,708,216 describes a measuring system for measuring the torque of a shaft. A ring is soldered onto the shaft""s periphery. An adjacent toothed disk, or encoder wheel, is provided for measuring speed. This disk is not suited for high speeds of rotation, since it is only secured by the ring to the shaft, and since the teeth of the disk produce an irregular and loud running performance.
The present invention is a measuring standard and a positional measuring device utilizing such a measuring standard, where the scale-graduation carrier is joined in a stable fashion to the base member, and where the area of the scale-graduation carrier bearing the scale graduation is not adversely affected by the joining process.
In one embodiment, the invention is a measuring standard comprising a drum-shaped base member, a prefabricated ring of a magnetic material having an inner surface area secured to a periphery of the base member by soldering, wherein a soldering material is introduced between the base member and the prefabricated ring. The measuring standard also includes a magnetic pattern arranged on a circular peripheral area of the ring, disposed opposite the soldered inner surface, having a series of alternating portions extending in the circumferential direction of the ring and whose magnetization differs on a portion by portion basis.
In another embodiment, the invention is a positional measuring device comprising a drum-shaped base member, a prefabricated ring having an inner surface area secured to a periphery of the base member by soldering, wherein a soldering material is introduced between the base member and the prefabricated ring, and a magnetic pattern arranged on a circular peripheral area of the ring, disposed opposite the soldered inner surface, having a series of alternating portions extending in the circumferential direction of the ring and whose magnetization differs on a portion by portion basis. The measuring device also has a magnetic field-sensitive scanning unit adjacent to the magnetic pattern, to scan the magnetic pattern and generate at least one electrical, positionally dependent sampled signal as a function of an instantaneous angular position of the base member.
The design of the present invention is advantageous because the scale-graduation carrier can be securely joined in a simple manner to the base member. The present invention can be used quite advantageously to secure a band-shaped or ring-shaped, magnetizable scale-graduation carrier to the periphery of a drum. This system is well suited for use at high speeds of rotation of the drum. With the present invention, the scale-graduation carrier does not become detached from the base member, even at high speeds.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.